We have developed a new experimental model of systemic lupus erythematosus in which autoantibodies against the 70K U1 RNP nuclear autoantigen, double-strand DNA and immune-deposit glomerulonephritis can be induced in BALB/c mice by immunization with an immunoglobulin light chain. This light chain belongs to a set of MRL-lpr/lpr monoclonal antibodies (Ab-2) recognized by monoclonal anti-68KU1 RNP polypeptide MRL-lpr/lpr antibody 28/12 (Ab-1). Monoclonal antibody 28/12 itself has an idiotypic marker of MRL-lpr/lpr anti-DNA antibodies. A sequence in the VL region of Ab-2 is homologous to an amino acid sequence in an antigenic region of the U1 RNP polypeptide. Our first priority is to define the structural basis of the Id-28/12 network. We have already begun a comprehensive examination of the structure of representative Ab-2's. We plan to establish whether a correlation exists between the amino acid sequences of these Ab-2's and their ability to evoke the production of autoantibodies in BALB/c mice. Any relationship to the antigenic region of the 70D RNP autoantigen will be of particular interest. Three major strategies will be employed: (a) sequencing of cDNA clones; (b) in vivo assays of immunoglobulins with known sequences and with quantitatively characterized immunochemical and idiotypic properties; and (c) immunization with synthetic peptides whose amino acid sequences correspond to those of the CDR3 light chain G. In parallel with these structural studies we are conducting an investigation of the serology, idiotypes, and immunopathology of the Id-28/12 network model. This part of the project, entails immunochemical and idiotypic analyses of serum and monoclonal antibodies as well as immunopathological investigations of relevant organs. Hybridomas obtained from mice immunized with Id-LGG will also provide material for sequencing the V genes of the evoked autoantibodies. Determination of these sequences will test the hypothesis that an idiotype can be the selective pressure driving a clonally related autoimmune response. We also plan investigations to determine if autoimmune responses to Id-LCG are MHC-restricted. Further studies of the spontaneous Id-28/12 network will be conducted in the MRL-+/+ mouse. We will examine the development over time of the Ab-1 and Ab-2 components of the network (i.e. which one appears first?), and analyze the frequency in young and old MRL-+/+ mice of monoclonal antibodies with VL CDR 3's related to the prototypic autoantigen-mimicking CDR3. We will also test the hypothesis that an immune response to Salmonella RE lipopolysaccharide can trigger the production of antibodies corresponding to the Ab-2 of the Id-28/12 network. The information we will obtain will be used for the development of new therapeutic strategies, with particular emphasis on the possibility of inducing (or restoring) immunological tolerance with synthetic peptides corresponding to autoantigen-mimicking epitopes of Ab-2.